1. Field of the Invention
The present invention relates in general to a method for measuring the cover thickness of a reinforcing bar in concrete by using stress waves.
2. Description of the Related Art
A very important parameter for the design of reinforced concrete is the cover thickness of reinforcing bars in the concrete, a variable which influences the development of the bond strength of the reinforcing bar, the width and distribution of the concrete cracks, and the durability of the concrete structure. Accordingly, in the assessment of structural safety, the cover thickness of reinforcing bars in concrete is always a main item.
The current methods for measuring steel reinforcing bars are all based on the principles of electromagnetic waves, and commercial measuring apparatuses thereof are available in the market. Referring to FIG. 1A, if reinforcing bars 92 in concrete 91 are arranged apart with a sufficient distance therebetween, then using the commercial measuring apparatuses 9 to measure the cover thickness of the reinforcing bars is effective (FIG. 1B). However, if the reinforcing bars in concrete are closely arranged as shown in FIG. 2A, then the reinforcing bars adjacent to the measured one interfere with the signals received. Analyzing the measured signals is very difficult because the signal interference is nonlinear, as shown in FIG. 2B. Unfortunately, the reinforcing bars in major concrete members, such as beams and columns, are always arranged very closely. Therefore, providing a means to effectively measure the cover thickness of a reinforcing bar in concrete is necessary.